This invention relates generally to the power supply systems that performs DC-DC conversion operations and more particularly, this invention relates to an energy storage circuit for a DC-DC converter of a wide input voltage range to operate the converter more efficiently with less capacitor at holdup time requirement applications.
It is becoming a demand to design a DC-DC converter for running at wide range of input voltage and for satisfying a holdup time when input voltage disappears. Generally, there are two approaches for designing these converters. One is two-stage approach, and the other is single-stage approach.
The two-stage approach includes a boost stage and a DC-DC stage. The boost stage converts the wide range input voltage to a fixed high voltage with holdup energy stored in high voltage DC bus capacitor, and the DC-DC stage provides DC output with an optimized design. The two-stage approach is known for its good performance such as low input current harmonics, small bulk capacitor for holdup time design, and optimized conversion efficiency. However, due to the additional boost power stage and its additional control circuit, the cost for components is increased, and size and weight are significantly increased. It is undesirable for low-power size-sensitive power supplies.
The single-stage approach is simple in circuit structure due to single DC/DC stage design. However, to satisfy required holdup time, the converter must be designed at minimum input voltage with a large number of input capacitors to store enough energy and a further extended input voltage range. The considerable number of input capacitors increases the overall size and the cost of the converter, and the extended input voltage range increases the rating of semiconductor and the cost of the converter and further lowers the overall conversion efficiency.
It is an object of the present invention to ensure high conversion efficiency of DC/DC converter for wide range of input voltage operation with holdup time requirement.
It is another object of the present invention to minimize storage capacitor for a given holdup time requirement.
It is a further another object of the present invention to lower the voltage rating and thus to lower the conduction loss of second side rectifier.
To achieve these objectives of the invention and in accordance with the purpose of the present invention, the present invention provides an energy storage circuit for a wide range of input voltage DC-DC converter with holdup time requirement. The energy storage circuit comprises (1) an energy storage capacitor, (2) a charging path including a diode connected in series with a current limiting resistor which is connected in series with the energy storage capacitor, (3) a discharging path including a parallel-coupled switch and a diode connected in series with a filtering inductor, coupled in series with said energy storage capacitor, and (4) a logic control unit coupled to the switch and is capable of turning the switch on and off.